1. Field of the Invention
The present invention relates to a curable composition that can be used in a paint, an ink, an adhesive, a pressure sensitive adhesive, etc., the composition having excellent adhesion to an organic polymer substrate. Furthermore, the present invention relates to a process for producing a cured coating having excellent adhesion to an organic polymer substrate.
2. Description of the Related Art
Among curable compositions, there are curable compositions that are cured by various types of energy such as light, heat, and an electron beam, and when improvement in the productivity of a production process (processing speed and reduction in the amount of energy applied) is taken into consideration, a photocurable composition and an electron beam-curable composition are suitably used.
As a photocurable composition, a radical polymerization system is often used, and from the viewpoint of improvement in productivity there is a demand for a radical polymerization system having high curing speed and higher sensitivity. As an attempt to increase the sensitivity of the radical polymerization system, various investigations have been carried out into photopolymerization initiators, polymerizable compounds, etc., and as high sensitivity polymerizable compounds, polymerizable compounds, etc. described in JP-A-2001-92127 and JP-A-2002-105128 have been disclosed (JP-A denotes a Japanese unexamined patent application publication). Furthermore, an attempt has been made to suppress inhibition of polymerization by oxygen in air, which is the main cause of lower sensitivity.
On the other hand, as an electron beam-curable composition a radical polymerization system is suitably used from the viewpoint of productivity. In the case of an electron beam, unlike light, since the generation of an electron beam has to be carried out under vacuum, inhibition of polymerization by oxygen is not an issue in the process. Furthermore, since a polymerizable compound receives the electron beam directly and starts to polymerize, the presence of an initiator is unnecessary. Moreover, due to the properties of an electron beam, when forming a coating, a reaction proceeds sufficiently with respect to the depth direction from the coating surface to the interface with a substrate, and there is the merit that the reaction proceeds rather easily at the interface with the substrate, which has high density of materials. In the case of light, with respect to the depth direction of a photocurable coating, light is absorbed on the coating surface and a reaction occurs easily, but it is difficult for it to proceed at the interface between the curable coating and the substrate.
However, on the other hand, in the case of a high output electron beam, there are the problems that chemical bonds of the substrate itself are broken, and particularly when an organic compound is used as the substrate, bond cleavage, etc. occurs, thus generating a gas, changing the chemical structure, or changing the physical properties of the substrate surface, and there is a recent trend to utilize a low energy electron beam. However, when a low output is employed, if a curable composition is made to have a high sensitivity that is at a level suitable for a production process, the structure of the polymerizable compound is limited to a structure that is suitable for polymerization by an electron beam.
That is, it is fundamentally important for a curable composition to give a polymerized coating that exhibits physical properties and functions in terms of tackiness, adhesion, elasticity, hardness, hydrophilicity, and electroconductivity, but since there is a restriction on the chemical structure of the curable compound, the variation thereof is narrowed, which is a serious problem.